The antihypertensive efficacy and safety of lisinopril, a long-acting angiotensin-converting enzyme inhibitor, were assessed in 23 patients with hypertension associated with impaired renal function (glomerular filtration rate 60 ml/min or less) in an open study of 12 weeks' duration. Lisinopril was given orally in single daily doses. The starting dose was 2.5 mg in patients with glomerular filtration rate (GFR) of less than 30 ml/min and 5 mg in all other patients. This was titrated to a maximum of 40 mg daily according to blood pressure response. A diuretic was then added if blood pressure was not controlled. Mean sitting and standing blood pressures were significantly reduced by lisinopril treatment. The median dose of lisinopril taken was 10 mg daily (range 2.5-40 mg), and only three patients required the addition of a diuretic. The mean glomerular filtration rate was unchanged during the study (38 +/- 16.4 ml/min at baseline, 41 +/- 21.0 ml/min after 12 weeks of treatment). Twenty-two patients completed the study. One patient was withdrawn because of nausea and vomiting due to reflux oesophagitis which was probably not drug related. Another patient had transient mild angioneurotic oedema and continued on lisinopril. No clinically significant haematological or biochemical changes were observed. In conclusion, lisinopril provided effective blood pressure control and was well tolerated in this group of hypertensives who are typically difficult to treat.